1. Field of the Invention
The present invention relates to noninvasive blood pressure measuring apparatus. In particular, the present invention is related to automatic noninvasive apparatus for providing measurement of systolic and diastolic blood pressures and pulse rate.
2. Description of the Prior Art
The most common method for determining blood pressure utilizes the Korotkoff sound technique. In this technique, an inflatable cuff is placed around the upper arm of a person and is inflated until the underlying artery is occluded. Pressure is then released gradually from the cuff until blood begins to pass through the artery. This passage of blood through the partially occluded artery produces Korotkoff sounds which may be detected by the use of a stethoscope or, in automated systems, by the use of a microphone. By monitoring the Korotkoff sounds and the cuff pressure, the systolic and diastolic pressures may be determined.
Systolic pressure is the pressure within the cuff at the time when a sudden increase in the intensity of Korotkoff sounds occurs. Diastolic pressure is the pressure at which a sudden reduction in intensity in Korotkoff sounds occurs.
While the detection of systolic and diastolic pressure can be performed manually, automation of this technique is clearly advantageous. Recently a number of automated blood pressure measuring systems have been developed. In many cases, these automated systems determine not only systolic and diastolic pressures, but also the pulse rate of the individual.
The following patents describe a variety of automatic or semi-automatic noninvasive blood pressure and pulse rate measuring devices. In most cases, the devices operate utilizing the Korotkoff technique.
Gillette et al U.S. Pat. No. 3,308,811 shows blood pressure measuring apparatus which processes the sounds from the microphone by passing the output of the microphone through a filter which passes a first band of frequencies until the systolic pressure is determined. The characteristics of the filter are then changed to pass a second band of frequencies which permit the diastolic pressure to be determined more accurately.
Anderholm et al U.S. Pat. No. 3,374,461 shows a physiological monitoring system which includes a transducer 23 for measuring both systolic and diastolic pressure and a transducer 24 for measuring pulse rate. The patent states (in column 5, lines 15-20) that pulse rate transducer 24 can be a separate transducer or the pulse rate can be measured by transducer 23. As described in column 9, lines 33-45, a logical AND circuit 199 is provided to ensure that the first indication of systolic pressure is not merely an artifact. After the first pulse rate is detected, another pulse must be sensed within two seconds if true systolic pressure has been sensed.
Funfstuck U.S. Pat. No. 3,400,709 shows a blood pressure monitor which uses a strain-gauge to produce a signal consisting of a DC signal responsive to the static blood pressure on which is superimposed an AC signal. The peak value of the AC signal is the systolic pressure and the negative peak of the AC wave is the diastolic pressure.
Edwards U.S. Pat. No. 3,405,707 shows a blood pressure measuring apparatus including a distinguishing system which responds to the difference between the energy level of the Korotkoff sounds and the noise level.
Wilhelmson U.S. Pat. No. 3,550,582 shows a portable blood pressure monitor. A cuff is inflated until the diastolic pressure is exceeded and the first Korotkoff sounds are sensed. The pressure in the cuff is then released until no further Korotkoff sounds are sensed (i.e. the pressure is below the diastolic pressure).
Burns et al U.S. Pat. No. 3,552,381 describes a technique for measuring diastolic blood pressure. A pressure is applied to the cuff which is sufficient to cut off arterial flow and negative-going pressure pulses are then applied which momentarily relieve the applied pressure in the cuff by predetermined amounts. These negative-going pulses are timed to coincide with the pressure minima of each pulse. Diastolic pressure is sensed when the pulse pressure minima overlaps sufficiently with the relieved applied pressure to permit spurts of arterial flow.
Croslin et al U.S. Pat. No. 3,581,734 shows a blood pressure measuring apparatus using a pair of cuffs, one for occluding the artery and the other for sensing. The systolic pressure is indicated only if a second pulse is detected within an expected time interval or window after a first detected pulse and if the second pulse is larger than the first pulse. After the systolic pressure has been sensed, the amplitude of each successive pulse is detected and the peak value is stored. The diastolic pressure is indicated after the systolic pressure has been sensed and only after a pulse is detected which has a peak value less than 0.7 of the largest peak value which has been detected and stored.
Sanctuary U.S. Pat. No. 3,654,915 shows a blood pressure measuring apparatus using a mercury column manometer and contacts for sensing the level of the mercury each time a Korotkoff sound signal is detected. Signal processing eliminates artifacts including Korotkoff sound signals which were neither preceded nor succeeded by another sound signal. Greenwood U.S. Pat. No. 3,717,140 shows a pulse rate measuring device including a counter which counts clock pulses between consecutive heart beats. The number of clock pulses counted is used to determine the pulse rate which is displayed.
Fernandez U.S. Pat. No. 3,744,490 shows a blood pressure measuring system which senses the systolic and diastolic pressures both on inflation and on deflation of the cuff. The electrical impedance between two body locations is also sensed and is used in controlling the valve for inflation and deflation of the cuff.
Rodbard et al U.S. Pat. No. 3,773,033 shows apparatus in which inputs are received from ECG electrodes, from a heart sound microphone, and from an arterial vibration sensor. The output of the system is displayed on a cathode ray tube.
Murphy, Jr. et al U.S. Pat. No. 3,779,235 describes an interface circuit which converts signals from a pressurometer to serial binary data representative of patient pulse rate and patient systolic and diastolic blood pressures.
Fletcher et al U.S. Pat. No. 3,814,083 shows a Korotkoff sound processor.
Gebben et al U.S. Pat. No. 3,850,169 shows analog circuitry for processing arterial pressure waveforms to detect the initial systole and dicrotic notch.
Page U.S. Pat. No. 3,858,574 shows a pulse rate meter which provides both a visual indication of each pulse beat and a digital readout of the pulse rate of a patient.
Nakayama U.S. Pat. No. 3,920,004 shows a noninvasive device which measures not only blood pressure, but also a variety of other parameters relating to blood flow.
Link et al U.S. Pat. No. 4,009,709 describes a technique in which the systolic pressure is sensed by phasing the pressure in a pressure cuff and measuring a quantity proportional to a time dependent fluctuating component representative of pulsatile pressure within the blood vessel. The systolic pressure is equal to the applied cuff pressure when the fluctuating quantity is about equal to one-half its maximum value.
Toda et al U.S. Pat. No. 4,062,277 shows a blood pressure measuring apparatus having two band-pass filters to separate the signal from the microphone into Korotkoff sounds and Sphygmus sounds. The systolic pressure is determined when two or more Korotkoff sounds correspond to the occurrence of the Sphygmus sounds. Similarly, the diastolic pressure is determined when Korotkoff sounds do not appear at successive times while Sphygmus sounds do occur.
Murawski et al U.S. Pat. No. 4,033,336 shows a system for sensing a variety of different medical characteristics. The system includes a blood pressure sensor shown in FIG. 14 and described in columns 17 through 20. The patent states that the cuff is gradually deflated at a predetermined rate by bleed valve 472, but provides no description of how the rate would be maintained constant.
Lee U.S. Pat. No. 4,069,815 provides a linear or uniform decline in pressure of the cuff during the deflation portion of the cycle. A constant volume reference container having rigid walls is linearally pressurized and depressurized with air to regulate the linear pressurizing and depressurizing of the flexible cuff.
Matsuoka et al U.S. Pat. No. 4,105,020 shows apparatus in which both pulse rate and blood pressure are measured automatically. The apparatus includes a pulse sound filter and a Korotkoff sound filter. The pulse rate measuring circuit commences counting pulses after at least two Korotkoff sounds have been detected. This counting continues until a predetermined number is reached. The pulse rate is determined by dividing the predetermined number by the time period required to count the predetermined number of pulses. The patent also describes an alternative embodiment in which the pulse sound signals are counted for a predetermined time period, and the number of pulses counted is divided by the predetermined time.
Lee U.S. Pat. No. 4,011,860 describes calibration of the pressure sensor in a blood pressure measuring system. A recalibration cycle occurs at the outset of each blood pressure measurement. During recalibration, a reference pressure is maintained and the output signal is adjusted until a reference level is reached.
Bugay U.S. Pat. No. 4,112,491 shows an analog computer which determines and displays pulsatile flow.
Huber et al U.S. Pat. No. D250,896 is a design patent showing a coin operated automatic blood pressure testing apparatus.